Hybrid vehicles may include an engine, a transmission and an auxiliary hydraulic pump for the transmission. The transmission requires a pressurized hydraulic fluid to operate, e.g., shift between different gear ratios. When the engine is operating, the engine powers a primary hydraulic pump that pressurizes the hydraulic fluid for the transmission. When the engine is not operating, the auxiliary hydraulic pump is engaged to provide the pressurized hydraulic fluid to the transmission. The auxiliary hydraulic pump is generally an electrically powered pump.
When the vehicle comes to a stop, the vehicle may initiate an auto stop/start engine protocol, which stops the engine when the vehicle is idle, and then restarts the engine when the vehicle begins to move again. When the engine is stopped in the auto stop/start engine protocol, the auxiliary hydraulic pump is engaged to provide the transmission with the pressurized hydraulic fluid required to shift the transmission into a first gear ratio, i.e., a low gear ratio, in order to prepare the vehicle for launch.
The transmission uses the pressurized hydraulic fluid to move a mode control valve between an “on” position and an “off” position. The mode control valve includes a spool, which is moved between the on position and the off position by hydraulic fluid pressure applied to either end of the spool. For example, to move the mode control valve into the on position, an electronic solenoid directs a fluid pressure to a first end of the spool, whereas to move the mode control valve into the off position, fluid pressure is applied to a second end, i.e., an opposite end, of the spool, while the electronic solenoid removes the fluid pressure from the first end of the spool. When the mode control valve is in the on position, the mode control valve engages a first clutch, which shifts the transmission into the first gear ratio. When the mode control valve is in the off position, the mode control valve engages a different clutch, which shifts the transmission into a different gear, i.e., a higher gear having a lower gear ratio. If the mode control valve and/or the auxiliary hydraulic pump fail when the engine is stopped, then the transmission may not shift into the first gear ratio in preparation for launching the vehicle, resulting in a high gear launch of the vehicle.
The vehicle operates diagnostic algorithms to determine if the auxiliary hydraulic pump and/or the mode control valve are functioning properly, i.e., to determine if the auxiliary hydraulic pump, the electronic solenoid and/or the mode control valve have failed or have not failed. If the auxiliary hydraulic pump fails, the vehicle may register an error code indicating that the auxiliary hydraulic pump has failed. Similarly, if the mode control valve or the electronic solenoid fails, the vehicle may register an error code indicating that the mode control valve or the electronic solenoid has failed.
In the event the auxiliary hydraulic pump has failed when the vehicle initiates the auto stop/start engine protocol and comes to a stop, the mode control valve may become “latched”. The mode control valve is latched when hydraulic fluid pressure is applied to the second end of the mode control valve before the hydraulic fluid pressure is applied to the first end of the mode control valve to move the mode control valve into the on position. When the mode control valve is latched, the mode control valve does not shift the transmission into the first gear ratio. Under these conditions, the diagnostic algorithms may falsely indicate that the mode control valve has failed and the auxiliary hydraulic pump has not failed, when in fact the auxiliary hydraulic pump has failed and the mode control valve has not failed, but is merely latched and being prevented from moving into the on position.